Compositions suitable for use as adjuvants in the preparation of vaccines, particularly those vaccines useful in the treatment of cancer, are provided. Methods for inhibiting tumor growth in an animal are also disclosed. Methods for immunizing an animal against cancer, such as prostate cancer, are also described. The adjuvants described are comprised of an extracellular matrix material, such as small intestinal submucosal (SIS) tissue. The preparations may take the form of sheets, gels, liquids (injectable), trocar, or other solid or semi-solid preparation. The invention provides for enhanced tumor inhibition of 2-fold or greater, compared to vaccine preparations without the extracellular matrix material, or from 4- to 5-fold, compared to preparations without the adjuvant promoting extracellular materials.